WASHINGTON (AP) — Set aside the high-pressure task of postseason pitching Chris Carpenter routinely masters for the St. Louis Cardinals and think about this:

Even the take-it-for-granted act of breathing feels odd on occasion now that he’s missing a rib and two neck muscles.

Taking the mound for only the fourth time in 2012 after complicated surgery to cure numbness on his right side, the 37-year-old Carpenter spoiled the return of postseason baseball to Washington by throwing scoreless ball into the sixth inning, and the defending champion Cardinals beat the Nationals 8-0 Wednesday to take a 2-1 lead in their NL division series.

Photo by The Associated Press

St. Louis Cardinals starting pitcher Chris Carpenter, left, is greeted by third base coach Jose Oquendo and teammates in the dugout after being relieved in the sixth inning of Game 3 of the NLDS against the Washington Nationals on Wednesday.

“To go from not being able to compete, and not only compete but help your team, to be able to be in this situation,” Carpenter said, “it’s pretty cool.”

Rookie Pete Kozma delivered a three-run homer, and a trio of relievers finished the shutout for the Cardinals, who can end the best-of-five series in today’s Game 4 at Washington. Kyle Lohse will start for St. Louis. Ross Detwiler pitches for Washington, which is sticking to its long-stated plan of keeping Stephen Strasburg on the sideline the rest of the way.

“We’re not out of this, by a long shot,” Nationals manager Davey Johnson said. “Shoot, I’ve had my back to worse walls than this.”

With the exception of Ian Desmond — 3-for-4 Wednesday, 7-for-12 in the series — the Nationals’ hitters are struggling mightily. They’ve scored a total of seven runs in the playoffs and went 0-or-8 with runners in scoring position and left 11 men on base in Game 3.

Rookie phenom Bryce Harper’s woes, in particular, stand out: He went 0-for-5, dropping to 1- for-15. He went to the plate with an ash bat and no gloves in the first inning, tried wearing anti-glare tinted contact lenses on a sun-splashed afternoon — nothing helped.

“Nothing I can do,” the 19-year-old Harper said. “I just missed a couple.”

All in all, quite a damper on the day for a Nationals Park-record 45,017 red-wearing, towel-twirling fans witnessing the first major league postseason game in the nation’s capital in 79 years. They didn’t have much to enjoy, in part because of the problems created by Nationals starter Edwin Jackson, who was on the Cardinals’ championship team a year ago.

“I didn’t feel like I was out of rhythm. I didn’t feel like I couldn’t throw strikes. I just missed across the plate with a couple of balls and it cost me,” Jackson said.

He gave up four consecutive hits in the second, the biggest being Kozma’s first-pitch homer into the first row in left off a 94 mph fastball to make it 4-0. Kozma took over as the Cardinals’ everyday shortstop in September, replacing injured All-Star Rafael Furcal, and only had 72 at-bats during the regular season.

But he’s only the latest in a series of “Who’s that?” stars of this postseason.

With the Capitol Dome rising beyond left field, the crowd of today was ready to root, root, root for the home team, breaking into chants of “Let’s go, Nats!” after player introductions and again after a four-jet flyover. And, boy, did they boo — when Cardinals outfielder Jon Jay was announced as the game’s first batter, when first-base umpire Jim Joyce missed a call, when catcher Yadier Molina trotted to chat with Carpenter, even when Carpenter paused between pitches to tie his red-and-gray right shoe.

“Carp’s been a dominant pitcher his whole career. Big-game pitcher. He showed up,” Washington’s Jayson Werth said. “He pitched well today. We had him in some spots. We had him on the ropes a couple of times. We were just one bloop away from a totally different ballgame.”

The Cardinals won 10 fewer games than the majors-best Nationals this season and finished second in the NL Central, nine games behind Cincinnati, sneaking into the postseason as the league’s second wild-card under this year’s new format. But the Cardinals become a different bunch in the high-pressure playoffs — no matter that slugger Albert Pujols and manager Tony La Russa are no longer around.

Carpenter still is, even though even he didn’t expect to be pitching this year when he encountered problems during spring training and needed what Cardinals manager Mike Matheny termed a “radical” operation in July to correct a nerve problem.

“Everyone had written him off, kind of,” Jay said. “It could have been a season-ending injury, where he could have just gone home and said, ‘See you later.”’

The top rib on Carpenter’s right side was removed, along with muscles that were constricting blood flow up there. After Wednesday’s game, he squeezed his big right hand with his left, explaining, “Basically, my nerves were getting squished down by all the scar tissue and all the muscles and everything. There wasn’t enough space.”

Still adjusting to the way breathing feels different, he returned Sept. 21, going 0-2 in three starts totaling 17 innings, so it wasn’t clear how he’d fare Wednesday.

Yeah, right.

Carpenter allowed seven hits and walked two across his 5 2/3 innings to improve to 10-2 over his career in the postseason. That includes a 4-0 mark while helping another group of wild-card Cardinals take the title in the 2011 World Series, when he won Game 7 against Texas.

“If the baseball world doesn’t know what an amazing competitor he is by now, they haven’t been paying any attention,” Cardinals left fielder Matt Holliday said.

Carpenter collected a pair of hits, including a double off the wall in the fifth that was about a foot or two away from being a homer. When he reached second base, he raised his right fist.

Earlier, Carpenter stepped to the plate for his first at-bat and chatted with umpire Joe West.

“I say hello to him. And he said hello back, and he talked about what a beautiful day it was to play a baseball game. And I was like, ‘You ain’t kidding,”’ Carpenter recounted. “Beautiful weather. The crowd is going crazy. ... There’s no question you take time to reflect on that.”

Notes: Holliday fouled a ball off his left leg in the eighth, stayed in to deliver a two-run single, then left for a pinch runner. ... Lohse beat the Braves in the wild-card game. ... Detwiler will be making the first postseason appearance of his career. His last regular-season start also came against the Cardinals, and he went only 2 1/3 innings, giving up seven runs. ... Wednesday was the 88th anniversary of Washington’s only World Series championship, won by the Senators on Oct. 10, 1924.